1. Field of the Invention
The present invention relates to a magnetic transfer device for magnetically transferring information carried by a master carrier to a slave medium, and more particularly to the structure of separating the slave medium from the master carrier after magnetic transfer.
2. Description of the Related Art
In magnetic transfer, a master carrier with a “land/groove” pattern (magnetic material) corresponding to information (e.g., a servo signal) is brought into intimate contact with a slave medium having a magnetic recording portion to which the information is transferred. In this state, a magnetic field for transfer (hereinafter referred to as a transfer field) is applied, and a magnetization pattern corresponding to the information carried by the master carrier is transferred and recorded on the magnetic recording portion of the slave medium. Such a magnetic transfer method is disclosed, for example, in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998)-269566.
The aforementioned magnetic transfer is serially performed on a plurality of slave mediums by employing a single master carrier. Initially, the master carrier is arranged in a magnetic transfer device, and a slave medium is conveyed to a position where it is brought into intimate contact with the master carrier. After the slave medium and the master carrier are brought into intimate contact with each other, a transfer field is applied to perform magnetic transfer. After the magnetic transfer, care must be taken when separating and removing the slave medium from the master carrier that they are not scored.
Particularly, during magnetic transfer, air is drawn from the contact surface between the slave medium and the master carrier to hold them in intimate contact with each other. Because of this, there are cases where the slave medium sticks fast to the master carrier after transfer. Since the sticking force is great, it is fairly difficult to separate the slave medium from the master carrier. When the slave medium and the master carrier are separated, there is a possibility that they will be scored. In addition, the separating operation is time-consuming and therefore reduces productivity.
The slave medium can be separated from the master carrier, by shifting the slave medium in the direction of the slave medium plane with respect to the master carrier after magnetic transfer, then projecting the edge of the slave medium from the edge of the master carrier, and chucking the projected portion. However, when shifting the slave medium with respect to the master carrier, there is a possibility that the master carrier and the slave medium will rub against each other and therefore they will be scored. If the master carrier is scored, it will cause poor magnetic transfer. If the slave medium is scored, it will result in a detective product.
In addition, the slave medium in intimate contact with the master carrier after magnetic transfer can be separated from the master carrier by sucking and holding the slave medium with the suction pad used in conveying the slave medium to the master carrier. However, in the case where the contact force between the master carrier and the slave member is strong, the separating force is insufficient, or there is a possibility of damaging the slave medium. Furthermore, the master carrier and the slave medium can be mechanically separated, or they can be separated by applying pressurized air to the contact surface therebetween.
However, even if the slave medium is separated from the master carrier, they will again stick to each other, unless the separated state is maintained. As a result, conveying becomes difficult.
In addition, in the aforementioned magnetic transfer method, if a transfer pattern (information) on the master carrier is magnetically transferred and recorded with the master carrier and the slave medium held in intimate contact, there are cases where the size and position of a magnetization pattern recorded on the slave medium differ from those of the transfer pattern (information) on the master carrier and therefore errors occur. The number of errors due to the pattern size fluctuation and positional shift varies with the position of the slave medium and the transferring time. However, the cause of the pattern size fluctuation has not been specified. In the case where there is a great fluctuation in the pattern size, for example, the tracking function cannot be sufficiently obtained if the signal recorded magnetically on the slave medium is a servo signal. As a result, reliability is reduced.
After magnetic transfer is repeated a large number of times, the master carrier surface is degraded. This degradation causes defects to occur in the signals recorded on the slave medium and considerably reduces the quality of transferred signals.
As indicated in experiments that is to be described later, magnetic transfer has been performed under various conditions with respect to the quality of transferred signals and it has been found that the temperature in the magnetic transfer step has a strong influence on a difference in pattern size between the master carrier and the slave medium before and after magnetic transfer. For example, the master carrier has an internal strain, which is not isotropic but anisotropic. Because of this, if ambient temperature changes, the anisotropy will cause distribution to occur in the amount of strain. Because of the distributed strain, local position shift occurs in both the transfer pattern on the master carrier and the magnetization pattern recorded on the slave medium and causes errors.
On the other hand, it has been found that missing signals, which occur in repeating magnetic transfer, occur due to contamination resulting from dust particles on the contact surface between the master carrier and the slave medium. The contamination has been analyzed and it has been found that there are roughly two kinds. One kind is due to the interposition of a metallic oxide. Basically, a metallic oxide is present on the master carrier surface, and it is the oxide of the magnetic layer material of the master carrier. Another kind is due to the interposition of ordinary dust particles, and a large number of dust particles are present on the slave medium surface. Furthermore, the two kinds of contamination vary with the weather and season when magnetic transfer is performed. Hence, investigations have been made with respect to the correlation between the contamination occurrence period and the environmental temperature and humidity, and it has been observed that there is a strong correlation between the contamination and the environmental humidity. In a low humidity environment a large number of ordinary dust particles are present, and in a high humidity environment the local oxide of the magnetic layer of the master carrier seems to occur frequently, although it is not a problem in appearance. It has also been found that a large number of dust particles adhere to the slave medium during conveyance, because static electricity is easily generated under a condition of low humidity. Furthermore, it has also been found that under a condition of high humidity, dew condensation occurs on the magnetic layer surface of the master carrier and oxides the magnetic layer surface, and that the oxide falls off the surface. Since most of the oxidized places occur at the acute-angle portions in a pattern formed on the master carrier, dew condensation under high humidity occurs at the acute-angle portions of the pattern, and consequently, the master carrier is selectively oxidized. Since the master carrier is partially oxidized, a difference in stress occurs between the oxidized portion and the unoxidized portion and therefore oxidized regions come off.